[Enhancement] Some improvements that may be necessary about xamlator

[ylatuya]

Hi!
Thanks for your feedback!
I believe the CloseCommand error would be the easier one to fix. The ErrorViewModel is missing that command property and it should be set before the preview, here:
https://github.com/ylatuya/XAMLator/blob/master/XAMLator.Server.Shared/Previewer.cs#L62
Using the command created here:
https://github.com/ylatuya/XAMLator/blob/master/XAMLator.Server.Shared/Previewer.cs#L25

For the DesingInstance instance we might need to register that extension somehow but I don't know how to do it honestly.

For the ControlTemplate issue, it's probably because pages are previewed with the PreviewPage class, which might not be supporting it, we should find a way to support it correctly.

[ChasakisD]

I will look to the binding warning, as far as I've got some free time.

During some research, ControlTemplate appears on the TemplatedPage which inherits from Page, while the PreviewPage is MultiPage< Page > and not MultiPage< TemplatedPage >

[ylatuya]

A solution would be to add the bindable property to the PreviewPage and forward it to the child page